Use create_task when executing the 'after' handler coroutine (#27)

* Use create_task when executing the 'after' handler coroutine

* use ensure_future for backwards compatibility

ocpp/v16/charge_point.py

@@ -205,7 +205,10 @@ async def _handle_call(self, msg):
 
         try:
             handler = handlers['_after_action']
-            await asyncio.coroutine(handler)(**snake_case_payload)
+            # Create task to avoid blocking when making a call inside the
+            # after handler
+            asyncio.ensure_future(
+                asyncio.coroutine(handler)(**snake_case_payload))
         except KeyError:
             # '_on_after' hooks are not required. Therefore ignore exception
             # when no '_on_after' hook is installed.